Studying the consequences of variation in individual life-histories is vital for our understanding of the evolution of animal societies. In this thesis, I study the ecology and consequences of group living on growth, survival, reproduction, and the gut microbiome of the Damaraland mole-rat (Fukomys damarensis), a subterranean cooperatively breeding mammal. For this, I used data and faecal samples collected from a long-term study population in the Kalahari Desert, South Africa.

I explored the effects of group size and group composition on individuals’ growth and survival. While large group size had no clear advantages for either growth or survival, individuals within groups biased to their own sex grew more slowly. The number of recruits increased modestly with group size, but experimentally created pairs showed the same reproductive success as established groups. Further, single individuals exhibited high survival rates and good body condition. Combined, these results suggest that mole-rats delay dispersal to maximise their own fitness, and that group living has costs and benefits for all group members.

I also investigated the effects of individual life-histories and group affiliation on the gut microbiome. This work shows that individuals bring the gut microbiome from their birth group when they disperse, and that group members have more similar gut microbiomes. When dispersed individuals start to reproduce in their new groups, they subsequently transfer this microbiome to their offspring, resulting in higher similarity between offspring with common descent of breeders. This pattern could arise from shared early life environment of breeders or through genetic relatedness of breeders. To separate the effects of these factors, I used a cross-foster experiment of captive animals, which showed that group members have more similar gut microbiomes, regardless of host relatedness.

My thesis gives deepened insights into the ecology of the Damaraland mole-rat. It shows how variation in the social environment of group living species affects their life-histories, their fitness, and beyond that extended phenotypic traits such as the gut microbiome composition.